Existing iris recognition systems are based upon the use of images from a single eye in which a presented iris image is compared to a database of iris images of enrolled people. See for example, U.S. Pat. Nos. 4,641,349, 5,291,560, 5,572,596, and 5,751,836. However, each person at the time of iris image capture for identification typically may have his or her head tilted at a different angle than at the time of acquisition of the reference iris image used for enrollment, resulting in the presented iris image for identification being rotated at some unknown angle relative to the reference iris image. The head tilt problem results in extra processing to account for such unknown relative rotation, especially for large databases of enrolled people. It would be desirable to substantially remove head tilt in iris images by using information provided from both eyes at the time of enrollment and at a time when iris images are captured for identification to avoid such extra processing, and thereby result in faster identification. In addition to improving processing time, head tilt information provided from two eyes can improve spoof detection of a fake iris and improve the speed and accuracy of eyelid segmentation.
Although a two eye pickup unit is described in U.S. Pat. No. 6,247,813, the unit processes each eye separately, and does not account for iris rotation due to head tilt. Further U.S. Pat. No. 7,248,720 uses information in addition to iris images for identification, but is limited to the extraction of information from the iris and retina of a single eye. U.S. Pat. No. 6,652,099 describes an apparatus for capturing both irises of a person in images and using both imaged irises in an iris recognition system, where the distance between the iris images of the both eyes is reduced to eliminate the space between the eyes, making more effective use of the available CCD area. U.S. Pat. No. 6,652,099 describes in its background that iris rotation cannot be determined from a single eye, and that the degree of iris rotation is obtainable to reduce comparative search times in iris recognition, but does not describe a method for readily enabling the determination of the degree of iris rotation or substantially removing the iris rotation problem when people's iris images are enrolled in an iris recognition system. Furthermore, U.S. Pat. No. 6,652,099 neither accounts for head tilt and thus iris rotation, nor any calculated interpupillary distance in the imaged eyes as a parameter in an iris identification system when comparing iris information stored in a database.
Prior art has accounted for iris rotation by relative rotation of iris images by translation of normalized polar templates of an iris image. Thus, comparative searching is performed over relative rotations between each template of iris reference images and the template of a presented iris image in a range of expected relative rotation. As stated earlier, this is a time consuming computational process, especially for large databases of templates of iris reference images. For example, each of the reference templates may need up to seven relative rotations with the presented template. Further, such methods for accounting for iris rotation have been applied to images of a single eye. See, for example, U.S. Pat. Nos. 7,298,874, 7,302,087, and 5,291,560.
International standards for exchange of iris image information have been established. These standards specify data formats for storage and exchange of iris data that includes information about rotation angle, see “Information technology—Biometric data interchange formats—Part 6: Iris image data”, ISO/IEC 19794-6, International Organization for Standardization, Geneva, Switzerland, 2005. However, such standard, like U.S. Pat. No. 6,652,099, does not relate to the removal of head tilt which caused the iris rotation angle in the first place at iris image capture at enrollment and for comparative searching.